<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Arguably the relational database concept is meant to avoid storing the same data more than once, but I have also done this to reduce overhead during complex output queries (ie storing a point on surface of a polygon instead of calculating it each time). Ultimately, it worked out slightly faster to have multiple smaller tables, as we only wanted one aspect of the geometry at any one time. When it came for time for others to use the same data, it was also much clearer to them what was going on.<div><br></div><div>It might be a good time to add that storing the same data in multiple formats requires some method to ensure concurrency - if someone updates the column that is in WGS84, a trigger to update the other columns would be essential to avoid returning mixed version information. This obviously holds true whether you have multiple columns in one table or multiple tables with one column each.</div><div><br></div><div>cheers</div><div><br></div><div>Ben</div><div><br></div><div><br></div><div><br><div><div>On 02/09/2009, at 3:13 , <a href="mailto:pcreso@pcreso.com">pcreso@pcreso.com</a> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>H Steve,<br><br>I have had recommendations that this is not good practice, but I have done this often myself for various reasons, with good success.<br><br>As far as I'm concerned, a very useful ability of a spatially enabled RDBMS is to realise that a geometry is only an attribute of an entity, like a date, time, numeric or string type. Real world entities can be represented by multiple geometries, and have multiple dates, etc, associated with them, so this is a perfectly good model, and offers substantial benefits over the (dated) GIS model where the geometry is somehow more special than other attributes of a feature/entity. <br><br>Cheers,<br><br> Brent Wood<br><br><br>--- On Wed, 9/2/09, <a href="mailto:Steve.Toutant@inspq.qc.ca">Steve.Toutant@inspq.qc.ca</a> <<a href="mailto:Steve.Toutant@inspq.qc.ca">Steve.Toutant@inspq.qc.ca</a>> wrote:<br><br><blockquote type="cite">From: <a href="mailto:Steve.Toutant@inspq.qc.ca">Steve.Toutant@inspq.qc.ca</a> <<a href="mailto:Steve.Toutant@inspq.qc.ca">Steve.Toutant@inspq.qc.ca</a>><br></blockquote><blockquote type="cite">Subject: [postgis-users] several SRID on one table<br></blockquote><blockquote type="cite">To: "PostGIS Users Discussion" <<a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a>><br></blockquote><blockquote type="cite">Date: Wednesday, September 2, 2009, 2:46 AM<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Hello,<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">We need to use a table for<br></blockquote><blockquote type="cite">several purposes<br></blockquote><blockquote type="cite">with different SRID.<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Is it a good practice to<br></blockquote><blockquote type="cite">have several<br></blockquote><blockquote type="cite">geometry columns on one table or should we create one table<br></blockquote><blockquote type="cite">per SRID?<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">What are the pros and cons<br></blockquote><blockquote type="cite">of using<br></blockquote><blockquote type="cite">several geometry columns on one table? <br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">thanks<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Steve<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Steve Toutant, M.<br></blockquote><blockquote type="cite">Sc.<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Analyste en géomatique<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Secteur environnement<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Direction des risques biologiques, environnementaux et<br></blockquote><blockquote type="cite">occupationnels<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Institut national de santé publique du Québec<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">945, avenue Wolfe<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Québec, Qc G1V 5B3 <br></blockquote><blockquote type="cite">Tél.: (418) 650-5115 #5281<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Fax.: (418) 654-3144<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><a href="mailto:steve.toutant@inspq.qc.ca">steve.toutant@inspq.qc.ca</a><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><a href="http://www.inspq.qc.ca">http://www.inspq.qc.ca</a><br></blockquote><blockquote type="cite"> <br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">-----Inline Attachment Follows-----<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">_______________________________________________<br></blockquote><blockquote type="cite">postgis-users mailing list<br></blockquote><blockquote type="cite"><a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br></blockquote><blockquote type="cite"><a href="http://postgis.refractions.net/mailman/listinfo/postgis-users">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><br></blockquote><blockquote type="cite"><br></blockquote>_______________________________________________<br>postgis-users mailing list<br><a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>http://postgis.refractions.net/mailman/listinfo/postgis-users<br></div></blockquote></div><br><div>
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